In today's post-genomic age, the analysis of gene functions in vivo is becoming more and more important. The analysis of gene functions using gene modified animals have been developed worldwide. This requires high level quality control of gene modified small animals, which increases demands for high standard animal breeding facilities.
In general, animal breeding systems used for experiments in scientific research require large-scale facilities and high level environment maintaining systems. Gene modification experiments, infection experiments and the like, which require isolation of a breeding facility from an external environment, prevention of infection of the external environment, and the like. Animal breeding system used for such experiments require special environment maintaining systems. Such special systems have defects of being complicated, costly, and requiring personnel expenses. Such special systems also have defects that a facility used for the system, once built, is not easily changed in design, cannot accommodate for an increasing number of animals, and cannot easily prepare different breeding conditions.
In the fields of experiments of recombinant DNA operations, infection experiments on bacteria and viruses, and the like, experimental animals such as mice, rats and the like are bred and managed under strict conditions. In order to achieve such strict conditions, large-scale facilities including breeding devices are required for breeding and managing the experimental animals. In addition, a significant amount of labor and cost are spent for breeding and day-to-day management of the experimental animals. Such large-scale facilities need to conform to strict criteria defined by public authorities such as national governments or the like (for example, the “Recombinant DNA Experiment Guidelines” announced by the Ministry of Education, Culture, Sports, Science and Technology (Notice by the Ministry of Education, Culture, Sports, Science and Technology dated Jan. 31, 2002)).
Currently, however, there is a shortage of such high standard breeding facilities for providing animal breeding environments due to, for example, the strict regulations. It is necessary to supply an animal breeding environment in each facility. Therefore, it has become costly to build the facilities, and the expenses for maintaining the facilities including the light and heat expenses and personnel expenses have become enormous. Since the breeding environment is designed to be large, a huge air-conditioning device is required, and costs for managing the facilities are higher than actually should be. The facilities which have been built must fulfill the strictly defined conditions and thus have a special structure. Therefore, it is difficult to refurbish the facilities or to use the facilities for other purposes. Especially, there is a shortage of special facilities for performing special experiments such as infection experiments. One reason is that it is difficult to maintain the high standards due to the large size of the breeding environments. Another reason is that a special environment for performing isolation needs to be separately prepared in order to perform special experiments such as infection experiments. In addition, there is a problem that when an infection accident occurs, a huge amount of cost and time are spent for cleaning the animals and removing the contamination.
Conventional facilities also have the following defect. Since animals have contact with the humans to an unnecessarily high degree due to the procedure of breeding experiments, the possibility of mutual infection between the animals and the humans becomes high. There is a high possibility of allergen sensitization to the humans, which generates an excessive load on the experiment operators.
Since conventional systems are not fully prepared for carrying the animals for isolation, there is a problem that the possibility of contamination to the animals and environmental pollution is increased when the animals are moved between breeders and the facilities, and between the facilities.
It is considered that there are about 400 research, experiment and breeding institutes handling experimental animals in Japan. Currently worldwide, small experimental animals are bred in metallic or polycarbonate-based breeding cages having floors covered with bedding. The bedding made dirty by the bred animals is disposed each time, and the breeding cages are used repeatedly after being washed and sterilized.
A conventional breeding cage for experimental animals has a shape shown in FIG. 29. A plurality of small projections 1504 are provided on the outer side walls of a main body 1501.
For example, a breeding facility in Osaka University, which is a middle-scale breeding facility, keeps about 10,000 mice a day (about 4,000 breeding cages). The bred animals are transferred to new breeding cages which are sterilized with steam (pulp is used as a bedding material) once a week or once every two weeks. Such a transfer is performed on a daily basis. Annually, about 230,000 breeding cages and about 22 tons of the bedding materials are necessary. About 35 tons of excrement needs to be disposed. About 900,000 liters of washing water and 5,700 Nm3 of town gas are used for these operations annually. This is a waste of a huge amount of resources in terms of labor and materials.
Especially in order to control the health condition inside the animal breeding cages, exchange of bedding materials, for example, is important and indispensable. Conventionally, the bedding materials have been exchanged manually. However, since the number of breeding cages for experimental animals is increasing and research using transgenic animals have been actively conducted recently, the costs for labor and materials for hygiene control tend to be more and more raised. There is another problem that the cages and bedding materials used for the breeding need to be prepared and disposed in the facility, and huge equipment for the preparation and disposal is required for each facility. Accordingly, a system for simplifying the work for hygiene control has been strongly desired.
For example, an experimental mouse usually bears one to several tens of babies at once, and the babies obtain a mating ability in 5 to 6 weeks after birth. Therefore, especially gene modified animals need to be individually bred from 4 to 5 weeks after birth, i.e., before the babies obtain a mating ability in order to maintain the strain. Demands for gene modified animals have recently been rapidly increased, and there are problems of increasing costs for labor and materials and a difficulty in obtaining breeding space.
Conventional facilities have many defects from the viewpoint of the operators who perform experiments using animals. For example, since the experiments need to be performed in a special facility as described above, the operator must enter the isolated breeding facility. The procedure for entrance is troublesome. There are strong desires to perform special experiments, such as gene modification experiments and infection experiments, which could conventionally be done only in experimental animal facilities, in usual laboratories. There is no conventional system satisfying such desires.